By default in Discourse, if a group grants a user a particular trust
level that is locked even if they are removed from the group.
With this new setting, when a user is removed from a group their
trust level is set to either the next highest trust level based on group
membership, or they are unlocked and promoted based on the default
mechanisms.
Group owners are regular users that can add or remove users to a group
The Admin UX allows admins to appoint group owners
The public group UX will display group owners first and unlock UI to
add and remove members
Group owners can only be appointed on non automatic groups
Group owners may not appoint another group owner
